Changes in plasma steroid levels and gene expression of pituitary gonadotropins, testicular steroidogenesis-related proteins and insulin-like growth factors during spermatogenesis of the yellowtail Seriola quinqueradiata

We have examined the annual cycle of spermatogenesis in captive yellowtail Seriola quinqueradiata , including the associated changes in both plasma 11-ketotestosterone (11-KT) level and gene expression of key endocrine factors, such as the pituitary gonadotropin subunits, testicular steroidogenesis-related proteins and insulin-like growth factors (IGFs), at different testicular developmental stages. Spermatogenesis was initiated in January, and all males had progressed to the spermiation stage in April. Plasma 11-KT levels and gene expression profiles were analyzed in relation to changes in histological findings. Plasma 11-KT levels increased during early to late spermatogenesis and were positively correlated with early mitotic divisions of spermatogonia leading to meiosis. The genes encoding the follicle stimulating hormone (FSH) beta subunit ( fshb ) and the luteinizing hormone (LH) beta subunit ( lhb ) both showed parallel expression patterns during spermatogenesis. A previous study revealed that FSH receptor mRNA in yellowtail testes is strongly expressed from early to late spermatogenesis, whereas levels of LH receptor mRNA peak during spermiation; only cyp17a1 [encoding cytochrome P450 17α-hydroxylase/C17-C20 lyase (P450c17)] transcript levels increased during early spermatogenesis. The expression patterns of the genes encoding testicular IGF-1 and -2 ( igf - 1 and igf - 2 ) differed from each other. Altogether, early spermatogenesis was associated with the regulation of 11-KT, which was probably induced by FSH through stimulation of specific steroidogenic enzymes, such as P450c17, and spermiation was considered to be triggered by LH. In addition, IGF-1 and IGF-2 are individually involved in spermatogenesis via autocrine/paracrine mechanisms.